Quantum mechanics and general relativity don’t fit together, and a big part of the issue comes down to gravity. For decades, the accepted route to an ultimate theory of everything has involved taking our best theory of gravity and squeezing it into the frame of quantum mechanics. Yet, almost a century later, scientists still haven’t managed to make gravity fit. Ivette Fuentes is a professor of quantum mechanics who conducts experiments at the scales where quantum theory and general relativity interplay. Fuentes sat down with ��è����Ƶ features editor Thomas Lewton to discuss the issues and fascinating theories that pop out when we try to fit classical and quantum mechanics together.

Read more: The experiments that could finally explain gravity

In December 2019, a bad tooth almost killed me. A terrible toothache turned into the biggest health crisis of my life, ultimately landing me in an intensive care unit for a week. Once I recovered, I had to make sense of why this happened to me. Personal negligence? Terrible luck? A fault of the US healthcare system? Rattled and unsure of how to feel, I turned to a place where I had long found answers to existential questions – quantum physics.

Physics is often considered to be humanity’s oldest science, getting its start with early astronomers. Much of our understanding of the world is built on physics as a solid, rigorous, objective foundation. It is a science that breaks the world into pieces, analyses each of them, then reassembles them all into a whole that we understand better. This process, based on empiricism and mathematics, doesn’t care about feelings. Physics isn’t personal: for example, regardless of who you are, you cannot escape a black hole. Yet I have always taken physics extremely personally.

In my book, , I invite the reader to do the same and, by showing how this benefited me, argue that making the objective subjective can be life-changing.

Take my bad tooth. Once the crisis was over, the issue that kept me up at night was essentially one of cause and effect. The effect was that I nearly died in the ICU, that much is clear, but what was the cause? In trying to process the event, I came up with several conflicting options. It was completely my fault because I dislike going to the dentist. It wasn’t my fault at all because I was a graduate student and couldn’t afford the dentist anyway. Trying to reconcile these two sequences of cause and effect only disturbed me further.

Relief unexpectedly came to me through chatting with physicists who study causality in the quantum realm. Reporting for ��è����Ƶ, I learned about the “quantum switch”, a procedure that allows a system to exhibit indefinite causality, where different sequences of cause and effect could exist at the same time through the quantum phenomenon of superposition. The idea is not without its critics, but experiments with particles of light have added credence to it. Some researchers have taken it as far as suggesting that the quantum switch should be built into emerging quantum technologies like quantum computers and batteries to make them work better.

As a physicist, I understand that I have very little in common with a��particle of light. Being macroscopic and warm, I am unaffected by the laws of quantum physics, while the photon can’t escape its quantum nature. Yet, thinking about the photon in the quantum switch, with its behaviour simultaneously dictated by “A causes B” and “B causes A” in a way that seems forbidden in every other arena, lessened my tooth conundrum.

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Maybe here, too, several conflicting ideas could be true at the same time. This brought me some peace and informed my future decision-making. I go to the dentist more now, and I believe that improving the working conditions of graduate students in the US, for example by providing them with dental insurance, is urgent and crucial.

In Entangled States, I describe a dozen examples like this, instances of quantum physics offering me guidance for something I couldn’t understand about my life and the world, or at least nudging me into thinking about it differently. I write about reckoning with my queerness, my experience of being a young immigrant, the way I build relationships, the way I used to teach high school students and much more, all in conversation with what I have learned about quantum physics both as a scholar and a reporter.

Being immersed in cutting-edge science, reporting from the border where human knowledge touches the unknown – which is exactly where quantum physics shines – undoubtedly changed me. Embracing its influence in an idiosyncratic and emotional way that complements the objective rigour of the science itself has improved my life and made me a better person. I highly recommend it. Instead of thinking about all things quantum as absolutely abstract and odd, do consider sometimes taking them personally.

On Q-Day, your privacy will be at stake. This is the moment when quantum computers break the encryption protecting the modern world, bank transactions become readable, private messages get exposed and even state secrets become vulnerable.

For years it sounded like sci-fi, something that was decades away from happening, if it happened at all. But now, research suggests that we may be hurtling towards Q-Day at a rapid speed.

In this video, ��è����Ƶ uncovers why many experts think the countdown to Q-Day may already have begun, and explains how quantum computers work and why these machines could both threaten the security of the modern world and unlock breakthroughs that could change our lives. Special thanks to Quantum Motion for letting us film at its facilities.

A large, cold molecule that resembles a butterfly, with “wings” made from electrons, has been made for the first time, completing the search for a “zoo” of similar molecules. The result could provide a gateway to completely new parts of the quantum realm.

at RPTU University Kaiserslautern-Landau in Germany and his colleagues made the molecule by cooling rubidium atoms to a few millionths of a degree above absolute zero by using lasers and electromagnetic forces. The researchers then used lasers again to make some atoms very large by pushing their outermost electron very far from their nuclei. The quantum properties of atoms that have been cooled and enlarged in this way can be precisely manipulated with lasers, which the team leveraged to move a giant atom’s electron towards a normal-sized rubidium atom, binding them together to create a new type of molecule with extreme properties.

Each molecule was about 25 nanometres in size – bigger than the diameter of a DNA strand that contains billions of atoms –��and thousands of times more responsive to electric fields than most molecules. The shape of the new molecule was determined by its electrons, with the outermost being spread out in space in a shape that resembles the wings of a butterfly.

Ott says that tuning the lasers just right to get molecules with this exact configuration was tricky – it took weeks of tweaking before the team successfully created them in the lab. Ott compares the process to searching for an object on a road by inspecting 1 millimetre at a time while standing a kilometre away.

Team member at Purdue University in Indiana says the work is a culmination of several past mathematical and experimental studies that helped narrow down this search. Based on mathematical models, researchers have spent 20 years searching for a “zoo” of giant ultracold molecules ought to exist, and the new butterfly is the last one to be discovered, he says.

At the same time, this experiment opens a path towards creating more exotic and elusive ultracold molecules, including those that could be very heavy in addition to being very large and charged, says at the University of Warsaw in Poland. at the University of Nottingham in the UK says the butterfly molecule was difficult to create but could now be used as precursor for making something even more difficult – ultracold atoms with negative charge, or anions. If made ultracold, anions could be used in tests of fundamental laws of particle physics or antimatter studies, but standard cooling methods have failed to chill them so far.

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Eiles and Ott have already mathematically investigated exactly how to use the butterfly molecule to create ultracold anions and hope to see the first signs of them within just a few years. “The theory is already written,” says Eiles.